N-vinylamides and process for preparing them



United States Patent 3,324,177 N-VINYLAMIDES AND PROCESS FOR PREPARING THEM Herbert Bestian and Harald Jensen, Frankfurt am Main,

Germany, assignors to Farbwerke Hoechst Aktiengesellsclraft vormals Meister Lucius & Bruning, Frankfurt am Main, Germany, a corporation of Germany No Drawing. Filed June 18, 1963, Ser. No. 288,615 Claims priority, application Germany, June 23, 1962, F 37,143 5 Claims. (Cl. 260-556) The present invention relates to new N-vinylamides and to a process for preparing them; more particularly, it relates to compounds of the formula wherein R represents a methyl or ethyl group and R stands for a methyl, ethyl or propyl group.

It is known that carboxylic acid and sulfonic acid amides of primary amines carrying another hydrogen atom at the amide nitrogen and lactams having an unsubstituted nitrogen atom can be converted in the presence of strongly alkaline catalysts with acetylene, under pressure, into the corresponding N-vinyl compounds.

This vinylation process for amides has hitherto been carried out under pressure only. Because of the risks which exist when working with compressed acetylene, expensive high pressure armatures are necessary for such a process, even when operating under pressures slightly above one atmosphere.

Furthermore, with this known pressure vinylation a smooth conversion takes place with cyclic lactams only. When applying the pressure process to acyclic, aliphatic carboxylic acid amides of the type of the N-methylacetamide and its homologues, the vinylation comes to a standstill after a low conversion. So, for example, with pressure vinlylation only 28% of N-vinyl-methyl-acetamide is obtained from N-methyl-acetamide. Besides, undesired tarry products are sometimes formed to a large extent by side reactions when acyclic amides are subjected to a pressure vinylation, whereby the yield and economy of the process are strongly impaired.

Now we have found a process for preparing N-vinylamides from acetylene and amides of the formula in which R and R represent aliphatic, cycloaliphatic, araliphatic or aromatic radicals, in which R and R may also be linked together to form a ring and in which Y stands for the carbonyl group CO- or the sulfonyl group SO in liquid phase in the presence of basic catalysts, wherein the reaction is carried out at a pressure between about 1 and 2.5 atmospheres and the vinylamide which is formed is removed from the reaction zone as it is formed. It was surprising that the vinylation, which is known to be carried out under high pressures only, can be practised at pressures within the range of one atmosphere or substantially lower. On the other hand, it was surprising that the longevity of the catalyst can be increased in the process of the present invention to such an extent that the conversion is almost quantitative with acyclic amides, too.

In the carboxylic acid amides of the formula the N-vinyl derivatives of which are sufiiciently volatile under the reaction conditions, R and R represent equal or diiierent, straight chain or branched, aliphatic or also isocyclic hydrocarbon radicals which have generally 1 3,324,177 Patented June 6, 1967 to 12 and preferably 1 to 7 carbon atoms and which, in the case of isocyclic radicals, have preferably 5 to 6 carbon atoms in the ring. R and R may be linked together so that the starting compound is a cyclic carboxylic acid amide having preferably 5 to 7 ring members.

Compounds which are capable of being vinylated, according to the process of the present invention, are, for example, N-methylacetamide, N-ethylacetamide, N-butylacetamide, N-methylpropionamide, N-ethylpropionamide, N-propylpropionamide, N-methylisobutyramide, N-butylbutyramide, N methyl-trimethylacetamide. Higher aliphatic homologues such as N-methyllauric acid amide or N-dodecylacetamide may be successfully vinylated, too. Furthermore, there are suitable N-cyclohexylacetamide, N methyl-hexahydrobenzamide, N methylbenzamide, acetanilide. Suitable lactams are pyrrolidone-Z, piperidone-2 and e-caprolactam and their derivatives substituted at the carbon atom by low molecular weight alkyl radicals.

Suitable sulfonic acid amides of the formula wherein R and R have the meaning given above are, for example, N-methyl-methane-sulfamide, N-methyl-ethanesulfamide and N-ethyl-propane-sulfamide.

As basic catalysts there are suitable, above all, alkali metals such as sodium and potassium and strongly basic compounds thereof such as sodium hydroxide, sodium amide, sodium methylate, sodium ethylate, sodium hydride, potassium hydroxide, potassium-tertiary-butylate. Particularly active are the alkali metal compounds of the amides used as starting compounds. In the conversion of N-methylacetamide, for example, there is preferably used sodium-'N-methylacetamide and in the conversion of pyrrolidone-Z the potassium salt of the pyrrolidone-Z. The alkali metal compound of the amides is preferably prepared in situ by dissolving one of the afore-mentioned alkali metal compounds in the amide to be vinylated.

For carrying out the process, excess acetylene is advantageously passed through the liquid mixture of the catalyst with the corresponding amide and heated to a temperature within the range of and 300 C., preferably and 250 C. The reaction temperature is suitably selected so that the N-vinylamide which forms is removed from the reaction mixture as quickly and completely as possible while the amide used as starting'compound is substantially retained. Thus the optimum temperature to be maintained in the zone of vinylation and the velocity of the gas current passed through are dependent on each other within certain limits. The vapors, which leave the reaction vessel together with the acetylene not used up, are condensed. From this condensate the N-vinylamide and unreacted starting amide are isolated by distillation, under reduced pressure if necessary, or by extraction or crystallization processes.

The process may be carried out batchwise, or in semicontinuous or continuous manner. The unreacted acetylene freed from condensable vapors is suitably recycled into the process while adding fresh acetylene. In the same manner, the unreacted starting amide can be continuously returned into the vinylation zone. Both the excessive acetylene and the unreacted starting amide, which is separated by a continuous distillation column, are preferably returned in a continuous manner into the vinylation zone, if necessary after previous mixing. In this case, the amount of fresh starting products corresponding to the amount of reacted acetylene and amide is additionally supplied in a continuous manner.

The catalyst is generally used in an amount ranging from 0.1 to 20 mol percent, preferably 1.0 to 10 mol percent, calculated on the amide used. With a continuous operation, it is often suitable to introduce part of the catalyst together with the amide supplied in a continuous manner.

The acetylene may be used in pure form or in admixture with inert gases, for example nitrogen.

The process is preferably carried out at atmospheric pressure. In exceptional cases it may be of advantage to work under slightly elevated pressure, for example up to 2.5 atmospheres gauge. With regard to the severe safety measures required for pressure reactions with acetylene, however, efforts are made to keep the excess pressure as low as possible. In some cases, especially when high boiling amides are used, it may be suitable to work under reduced pressure.

Because of improved yield, the process of the present invention permits a more economical preparation of acyclic vinylamides than is possible with prior art processes. A particular advantage is that pressure apparatus and safety measures which are required when working with compressed acetylene need not be used. Thus, vinylamides have become easily accessible. The method is also suitable for working on a laboratory scale. Some products according to the present process are novel substances, viz N-vinyl-N-ethylacetamide, N-vinyl-N-methylpropionamide, N-vinyl-N-ethylpropionamide and N-vinyl- N-methylisobutyramide.

The vinylamides are valuable starting materials for plastics, emulsion stabilizers, textile auxiliaries, cosmetics, pesticides and pharmaceutical products.

The following examples serve to illustrate the invention but they are not intended to limit it thereto. Prior to beginning the tests, all apparatuses were freed from oxygen by purging with nitrogen.

Example 1.N-vinyl-N-methylacetamide (a) In a four-neck flask provided with stirrer, gas inlet pipe, internal thermometer and a condensing tap, 21 current of 150 liters per hour of acetylene was passed, at 180 C. and at normal pressure, while vigorously stirring, through a solution of 4.5 g. of potassium-N-methylacetamide in 295.5 g. of N-methylacetamide prepared by dissolving 1.6 g. of potassium in 298.4 g. of N-methylacetamide. Within 90 minutes there were obtained 294.4 g. of a condensate from which 35.2 g. of N-vinyl-methylacetamide were obtained by distillation under reduced pressure. Boiling point at 20 mm. of mercury=63.8 C.; n =1.4827. 258 g. of unchanged N-methylacetamide were recovered, while 12.5 g. of residue remained in the I reaction flask.

(b) A heatable Inultineck fiask provided with stirrer, gas inlet pipe, internal thermometer and a supply pipe reaching down to the bottom was connected via a well isolated vapor pipe with a separator from which the gases coming out of the flask could escape upward to an effective cooler. The condensate flowed downwards to the middle of a suitably dimensioned distilling column having a total height of 80 cm. The sump product leaving this column flowed back through the feed pipe into the reaction flask. Through the same pipe the supply of N- methylacetamide was replenished from a dropping tunnel in proportion to its conversion. The N-vinyl-N-methylacetamide was collected at the head of the distilling column. The acetylene leaving the separator and the cooler was recycled through the inlet pipe into the reaction flask by means of a gas pump, the consumed gas being replenished and a little part being let off as exhaust gas. 2.00 kg. of N-methylacetamide were introduced into the reaction flask in which 20 g. of sodium amide had previously been dissolved While pumping off the ammonia. Through the mixture heated to 170 C., there were passed 600 liters of acetylene per hour, at about normal pressure. During the course of 30 hours, there were added thereto a total of 3.88 kg. of N-methylacetamide in which 1 1 150 g. of sodium amide had previously been dissolved with degassing, while 4.58 kg. of N-vinyl-N-methylacetamide of 99% strength distilled oil at the head of the column. The test was then discontinued without the vinylation being abated. For calculating the conversion, the content of the reactor and the sump of the column (2.57 kg.) were distilled whereby 1.57 kg. of methylacetamide were recovered.

Considering the fact that 0.31 kg. of the methylacetamide used were bound in the catalyst, the conversion amounted to 72% and the yield to of the theoretical.

Example 2.N-vinyl-N-ethylacetamide In the apparatus described in Example 1a, there were passed, at 190 C., and at about 1 atmosphere, liters of acetylene per hour through a reaction mixture obtained by dissolving 1.8 g. of sodium in 341 g. of N-ethylacetamide. There were obtained 320 g. of condensate which yielded by distillation 27 g. of N-vinyl-N- ethylacetamide having a boiling point at 18 mm. of mercury of 69 C., (n =l.4750).

Analysis.C H NO (113.2) calculated: C, 63.7; H, 9.8; N, 12.4. Found: C, 63.5; H, 9.4; N, 12.5. By catalytic hydration, diethyl-acetamide was obtained therefrom.

Example 3.-N-vinyl-N-methylpropionamide In the apparatus described inExample 1a, there was passed, at 190 C., and at about 1 atmosphere, a current of liters of acetylene per hour through a solution of 2.3 g. of sodium in 435 g. of N-methylpropionamide. From the condensate (421 g.) were obtained 47 g. of N-vinyl-N-methylpropionamide. Boiling point at 13 mm. of mercury=69 C.; n =1.4797.

Analysis.-C H NO (113.2) calculated: C, 63.7; H, 9.8; N, 12.4. Found: C, 64.0; H, 9.9; N, 12.4.

Example 4.-N-vinyl-N-ethylpropionamide By the same process as described in the foregoing examples, there were obtained from a solution of 2.3 g. of sodium in 505 g. of N-ethylpropionamide, at a temperature ranging from to 200 C., with an acetylene current of 150 l./h., 494 g. of distillate which yielded 69 g. of N-vinyl-N-ethylpropionamide. Boiling point at 12 mm. of mercury=74 C.; n =1.4737.

Analysis.-C H NO (127.2) calculated: C, 66.1; H, 10.3; N, 11.0. Found: C, 66.2; H, 10.1; N, 11.0.

Example 5.N-vinyl-N-methyl-isobuzyramide After having pumped ofi the ammonia formed, a solution of 4.7 g. of sodium amide in 405 g. of molten N- methylbenzamide was treated, as described in Example 1a, at a temperature within the range of 220 and 230 C. with an acetylene current of 3001./h. at about normal pressure. The condensate (319 g.) yielded by distillation under reduced pressure 94 g. of N-vinyl-N-methylbenzamide. Boiling point at 14 mm. of mercury=137 to 139 C.; n =1.5670.

Example 7.N-vinylpyrrolid0ne In the apparatusdescribed in Example 1 200 liters of acetylene were passed, at a temperature within the range of 210 to 230 C. and at about 1 atmosphere through a solution of 6.3 g. of sodium in 425 g. of pyrrolidone-2 until no more amide passed over. The condensate (392 g.)

Example 8.N-vinyl-N-methyl-methane-sulfamide 600 liters of acetylene per hour were passed at 200 C. and at about 1 atmosphere, and as described in EX- ample 1a, through a solution of 64.5 g. of sodium-N- methyl-methanesulfamide (0.5 mol) in 1015 g. of N- methylmethane-sulfamide (9.3 mol), prepared by dissolving 11.5 g. of sodium in 1070 g. of N-methylmethanesulfamide. Within 4 /2 hours, 1026 g. of condensate passed over, while 80 g. of substance remained undistilled. From the condensate there were obtained by distillation under reduced pressure, in addition to 699 g. of starting amide, 291 g. of pure N-vinyl-N-methylmethane-sulfamide. Boiling point at mm. of mercury: 99 C.; n =l.4701. This result corresponded to a conversion of 31% and a yield of 75%.

Analysis.-C H NO S (135.2) calculated: N, 10.4; S, 23.7; hydrogenation iodine number 188. Found: N, 10.7; S, 23.5; hydrogenation iodine number 188.

Example 9.N-vinyl-N-ethylacetamide The apparatus described in Example 1b was charged with 1000 g. of N-ethylacetamide in which 14.5 g. of sodium amide were dissolved while the ammonia set free was removed. 700 liters of acetylene per hour were passed at 170 C. and at about normal pressure through the mixture. During 43 hours there were added a further 4.67 kg. of ethylacetamide in which 163 g. of NaNH were dissolved, and 4.49 kg. of N-vinyl-ethylacetamide were distilled off at the same time. From time to time a portion of the reactor content was removed in order to avoid a concentration of the sodium salts. Fromthese quantities and the remaining reactor content, there were recovered 1.44 g. of ethylacetamide. Thus, the conversion was 75% and the yield amounted to 82%.

Example 10.N-vinyl-N-methyZpropionamide In the same manner as described in Example 1b and 9, there were prepared in 34 hours, from 4.66 kg. of N- methylpropionamide and 118 g. of sodium amide, 2.96 kg. of N-vinyl-N-methylpropionamide in a reactor having a content of 1 1., at a reaction temperature of 175 C. and an amount of 700 liters of acetylene per hour. 1.34 kg. of starting amide were recovered. Conversion: 72%; yield: 69%.

Example 1I.N-vinylpyrr0lid0ne According to the processes described in Examples 112, 9 and 10, there were obtained in 27 hours, from 6.07 kg. of pyrrolidone and 80 g. of sodium amide, 4.47 kg. of N-vinylpyrrolidone at 190 C. and with 1050 liters of acetylene per hour. 1.79 kg. of pyrrolidone were recovered. Thus, the conversion amounted to 70% and the yield to 80% Example 12.N-vinyl-N-isopropylacetamide As described in Examples 111, 9, 10 and 11, the solution of 110 g. of sodium amide in 3.79 kg. of N-isopropylacetamide was reacted at 170 C. and with a circulation of 600 liters of acetylene per hour. 2.175 kg. of starting amide were recovered and 1.12 kg. of N-vinylisopropyl acetamide were obtained. The result corresponded to a conversion of 42% and to a yield of 55%. Boiling point at 15 mm. of mercury=69 C.; n =1.4645.

We claim:

1. In a process for preparing compounds of the formula wherein X is a member selected from the group consisting of carbonyl and sulfonyl, R is lower alkyl, R is a member selected from the group consisting of lower alkyl and phenyl, and R and R together are lower alkylene, which process comprises reacting acetylene with an amide of the formula wherein R R and X are defined as above, in liquid phase and in the presence of a basic catalyst, the improvement of passing gaseous acetylene at a pressure between 1 and 2.5 atmospheres through said amide and removing the N-vinylamide product from the reaction zone in vapor form as it is formed.

2. A process as claimed in claim 1, wherein the reaction is carried out at a temperature between and 250 C.

3. A process as claimed in claim 1, where in an alkalimetal salt of the amide employed as starting material is used as catalyst.

4. A process as claimed in claim 1, wherein unreacted acetylene and unreacted amide escaping from the reaction zone are continuously recycled to the reaction zone.

5. A process as claimed 1, wherein the catalyst is used in amounts between 1.0 and 10 mol percent, calculated on the amide used.

References Cited UNITED STATES PATENTS 2,317,804 4/1943 Reppe et a1. 260-561 X 3,008,992 11/1961 Lynn et al 265561 OTHER REFERENCES Bailey et. al.: Journal Org. Chem, vol. 23, pages 996- 1001 (1958).

Encyclopedia of Chemical Technology, vol. 11, pp. 648-49, 656-657 (1953).

Reppe et al.: I Justus Liebigs Ann. der Chem., vol. 601, pages 128 thru 138 (1956).

Wuesthoif et al.: 1,129,946, May 24, 1962, 260-561, Germany Auslegeschrift.

Hausemann: 1,088,479, Sept. 8, 1960, 260-561, German Auslegeschrift.

Auslegschrift, No. 1,088,479 (German), 5/62, to Wuesthoff et a1.

WALTER A. MODANCE, Primary Examiner.

NICHOLAS S. RIZZO, Examiner.

ROBERT L. PRICE, HARRY I. MOATZ,

' Assistant Examiners. 

1. IN A PROCESS FOR PREPARING COMPOUNDS OF THE FORMULA 